1. Field of the Invention
The present invention relates to an inertial drive actuator.
2. Description of the Related Art
When a drive pulse with a waveform having a moderate rise and a subsequent steep fall is applied to a piezoelectric element, which is a kind of electro-mechanical transducer, the piezoelectric element expands slowly at the moderate rise of the drive pulse and contracts quickly at the steep fall of the drive pulse. There is a known inertial drive actuator that utilizes such characteristics. In the inertial drive actuator, drive pulses having the above described waveform are applied to a piezoelectric element to generate vibration having different speeds in the directions of expansion and contraction in the piezoelectric element thereby causing a drive member fixed to the piezoelectric element to reciprocate at different speeds. Thus, a movable member in frictional contact with the drive member is moved in a predetermined direction.
Japanese Patent Application Laid-Open No. 2003-185406 discloses an inertial drive actuator having a function of detecting the position of a movable member. This inertial drive actuator is shown in FIG. 17. The inertial drive actuator 100 has a piezoelectric element 120, one end of which is fixed on the frame 110 of the actuator by, for example, adhesion. A drive shaft 130 is fixed on the other end of the piezoelectric element 120 by, for example, adhesion. A movable member 140 is in frictional contact with the drive shaft 130. A detection member 150, which constitutes a fixed electrode used to detect the position of the movable member 140 based on capacitance, extends parallel to the moving direction of the movable member 140 while being kept away from the movable member 140. The detection member 150 is fixed on the frame 110. The drive shaft 130, the movable member 140 and the detection member 150 are made of electrically conductive materials. The detection member 150 has projections and depressions that are arranged at regular intervals along the moving direction of the movable member 140 on its surface facing to the movable member 140 to constitute an electrode 151. The electrode 151 and the movable member 140 constitute a capacitor with a gap D therebetween.
When assembling the above described inertial drive actuator 100, the drive shaft 130 and the detection member 150 are required to be assembled in such a way that the spacing and degree of parallelization therebetween is kept within an allowable range. This is because variations in the gap (i.e. spatial variations and changes with time) between the electrodes that constitute a capacitor can deteriorate the detection accuracy in the position detection utilizing capacitance.
In the above described inertial drive actuator 100, however, since the drive shaft 130 and the detection member 150 are provided as separate members, it is difficult to arrange them with good accuracy in terms of the above described spacing and parallelization while paying attention to their axes. Thus, such requirements have been factors that deteriorate efficiency in assembling.